1. Field of the Invention
This invention relates to magnetic resonance imaging (MRI) utilizing nuclear magnetic resonance (NMR) phenomena. It is particularly directed to MRI systems and methods utilizing a C-shaped main polarizing magnet with opposing pole faces situated in approximately parallel horizontal planes above and below the image volume. Still more particularly, this invention is directed to method and apparatus for the transport of a patient into the image volume of such a C-shaped MRI magnet structure.
2. Related Art
MRI is now a well-known and commercially available technique for non-invasive imaging of patient tissue. Although there are many different species of MRI systems now available, all of them require a relatively massive polarizing magnet for producing a nominally static, nominally uniform NMR polarizing field within the volume to be imaged. Additional pulsed electromagnet gradient coils are utilized in conjunction with pulsed RF fields (via an RF antenna coil) to acquire raw MRI data (as NMR RF responses) during an imaging procedure. The raw data may be transformed into a visual image that represents the spatial distribution of NMR nuclei within the image volume (e.g., representing patient tissues) by a number of known procedures (e.g., via multiple Fourier Transformation).
One presently popular MRI system design utilizes a cryogenic solenoidal superconducting electromagnet to create the nominally static nominally uniform polarizing magnetic field. In such a design, the bore of the solenoid is of extended length and diameter so that the whole body of a patient may be transported completely within the bore during imaging procedures. This leaves essentially no access to the patient during preliminary procedures or during final imaging procedures. It also may provoke claustrophobic reactions in some patients and can interfere with the continuance of life support measures and the like which may be required by the patient. It further prevents almost any interventional procedures which attending medical personnel might wish to perform on the patient while in the image volume.
Another currently popular MRI system design utilizes permanent magnets in conjunction with substantially horizontal pole pieces that are opposingly disposed above and below the image volume. A return magnetic flux flows between the two poles via a plurality of vertical support members disposed at intervals (e.g., 90.degree. intervals) around the periphery of the poles. This leaves substantially more open access to the image volume during preparatory and imaging procedures so as to permit interaction with the patient. It also tends to leave the patient in more of an "open" environment and thus lessens the likelihood of claustrophobic reactions. One such MRI system is described more particularly, for example, in commonly assigned U.S. Pat. No. 4,829,252 to Kaufman, the entire content of which is hereby incorporated by reference.
There have also been other approaches to a more "open" structure for the main polarizing magnet of a MRI system. Some examples are included in the following references (the entirety of each of which is hereby incorporated by reference):
U.S. Pat. No. 4,534,358--Young (1985)
U.S. Pat. No. 4,985,678--Gangarosa et al (1991)
U.S. Pat. No. 5,008,624--Yoshida (1991)
British GB 2,215,522A--McGinley (1989)
Japanese Patent Appln. 62-26052--Oikawa (1987)
With respect to side-loading patient transport mechanisms having relevance to this invention, the most pertinent of the above references is probably the Japanese application 62-26052 to Oikawa. Here, Oikawa does teach side-loading patient transport apparatus for use with a C-shaped main MRI polarizing magnet. However, Oikawa cantilevers the patient bed on a wide base pedestal which remains as a substantial obstruction between any attending personnel and the patient after the patient has been side-loaded into the image volume. Thus, although there is still some accessibility to the patient during preparatory and imaging procedures, the attending personnel would have to inconveniently lean over the wide base pedestal unit to reach the patient in the imaging volume. Accordingly, this prior approach still fails to provide advantageous substantially adjacent open accessibility to the patient.